You do not need to do more. The mere fact that they are suspended will prevent any non operational email to be sent to them.
Yet operational emails (such as a registration confirmation) will still be sent.
Yes, this is reversible. Just uncheck the "Marketing suspended" checkbox.
Hey Steph, when you mark someone as Marketing Suspended, they will stop receiving any emails from you. This is permanent until you make a change to that field on their record sometime in the future.